This application is based on Japanese Patent Applications No. 2002-109172 filed on Apr. 11, 2002 and No. 2003-24353 filed on Jan. 31, 2003 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a failure diagnosis method and failure diagnosis device for an evaporated fuel treating unit and in particular, to a technology for making a determination on the leak of fuel vapor.
2. Description of Related Art
The evaporated fuel treating unit is a unit for preventing evaporated fuel produced in a fuel tank from being discharged into the atmosphere. A combined body of structural members including the fuel tank, a canister, a purge passage, and a purge control valve forms a closed space when the foregoing purge control valve is closed. This closed space is called an evaporation system. It is desired to mount a failure diagnosis device for determining whether or not evaporated fuel leaks from the evaporation system. Hereinafter, the failure diagnosis device and it""s function may be referred to as leak check.
JP-A-5-272417, and U.S. Pat. No. 5,146,902 discloses a method in which pressure in the evaporation system is increased by a pump and then the state of decrease in the pressure in the evaporation system is measured at a specified time set previously to determine the state of leak. However, according to this method, the volume of a space to be pressurized is varied by the amount of remaining fuel and hence the rate of decrease in the pressure is also varied, so that it is possible to detect whether or not leak occurs but impossible to correctly detect the magnitude of the leak. Further, since the state of decrease in the pressure is varied also by differences in the atmospheric temperature and the properties of the fuel, it is impossible to determine the state of the leak sufficiently correctly if no correction is made. For example, the atmospheric temperature and the properties of the fuel affect the amount of evaporated fuel at a certain temperature. In order to grasp the state of the leak correctly, it is thought to correct the state of the leak by parameters affecting the determination such as the amount of remaining fuel but this makes the determination complex and hence increases cost. On the other hand, if stricter conditions for allowing the leak check are become stricter, it is impossible to achieve an essential object of ensuring the frequency of determinations.
On the other hand, JP-A-10-90107 discloses a method in which a pump is driven until operating characteristic values such as current, voltage, the number of revolutions are saturated and the saturated operating characteristic values are compared with the base values to determine the state of leak. However, according to this method, the pump is driven until the operating characteristic values are saturated and hence time to drive a pump is elongated, which degrades fuel consumption. Moreover, it is necessary to use a long-life pump or to increase the frequency of replacements of the pump and hence to increase cost.
Still further, JP-A-11-351078 discloses a method of using a base orifice. Variations in pressure in the evaporation system in this technology are shown in FIG. 19. The state of decrease in the pressure in the evaporation system from the time when the pressure is increased to a specified pressure P0 to the time when a previously set time T elapses is measured in a case where leak occurs at an orifice as a base leak point and in a case where leak does not occur. The pressure changing state may be measured as pressure differences P1, and P2. The amount of change in the pressure P2 caused by a leak hole as a failure is compared with the amount of change in the pressure P3=P1xe2x88x92P2 caused by the orifice as the base leak hole thereby to cancel effects produced by the amount of remaining fuel, atmospheric temperature, fuel properties, and the like.
However, in this method, when the amount of remaining fuel is extremely large, that is, the volume of the space to be pressurized is extremely small, as shown in FIG. 20, the rate of decrease in the pressure is increased to make the pressure zero, atmospheric pressure, that is equal to the pressure outside the evaporation system before the foregoing time T elapses. This is not the proper amount of change in pressure. On the other hand, when the amount of remaining fuel is small, the rate of decrease in the pressure is decreased to make it impossible to produce the sufficient amounts of change in pressure P1, P2 and hence to produce a sufficient detection accuracy. For this reason, there is a fear that correct determination can not be made on the state of leak. If the pressure in the evaporation system is sufficiently increased, the state of leak can be correctly determined but there are raised a problem that a fuel tank and the like need to have sufficient resistance to pressure and a problem that the capacity of a pump for increasing pressure needs to be increased. These problems can not be easily solved.
Still further, JP-A-11-351078 discloses a method of measuring time required for the pressure in the evaporation system to decrease by a specified amount of pressure drop. The measurement of time can be easily performed with higher accuracy than the detection of pressure. However, the determination method based on the amount of changes in the pressure P1, P2 can not be used for the determination based on the required time. For this reason, in order to put the method of leak check utilizing the required time into practical use, some improvements need to be made that are not disclosed in JP-A-11-351078.
The present invention has been made in view of the above circumstances. It is the object of the invention to provide a failure diagnosis method and a failure diagnosis device of an evaporated fuel treating unit by which a correct leak check can be performed regardless of the amount of remaining fuel and practically.
In accordance with the first aspect of the invention, there is provided a failure diagnosis method for diagnosing an evaporated fuel treating unit, which comprises the steps of: producing a pressure difference between inside an evaporation system having a fuel tank, the canister, the purge passage and the purge control valve and outside the evaporation system; measuring the state of change in pressure in the evaporation system; and determining the state of leak in the evaporation system based on the measured state of change in pressure.
In the method: a pressure in the evaporation system is made a first specified pressure, then a base leak hole is opened, and a first required time is measured that is required for the pressure in the evaporation system to change from the first specified pressure to a second specified pressure set at a value closer to a pressure outside the evaporation system in a state where leak occurs at the base leak hole and a leak hole as a failure;
the pressure in the evaporation system is made the first specified pressure, then the base leak hole is closed, and a second required time is measured that is required for the pressure in the evaporation system to change from the first specified pressure to the second specified pressure in a state where leak occurs only at the leak hole as a failure; and
the state of the leak in the evaporation system is determined by comparing the second required time with a determination base time obtained by multiplying the first required time by a coefficient set previously based on the area of the base leak hole.
In the first measurement of the first required time, the leak points of the evaporation system are the leak hole as a failure and the base leak hole and in the second measurement of the second required time, the leak point is only the leak hole as a failure. Thus, the required time that is required for the pressure in the evaporation system to change from the first specified pressure to the second specified pressure is larger at the time of the second measurement in which the area of the leak point is smaller. According to the Bernoulli""s theorem, the velocity of flow of gas at the leak point is equal if the pressure in the evaporation system is equal. Thus, the ratio of the foregoing second required time to the foregoing first required time is equal to the ratio of the area of the leak points at the time of the first measurement to the area of the leak point at the time of the second measurement.
Here, the ratio of the area of the leak points at the time of the first measurement to the area of the leak point at the time of the second measurement depends on the ratio of the area of the leak hole as a failure to the area of the base leak hole which causes leak only at the time of the first measurement.
Thus, by setting the foregoing coefficient on the basis of the area of the base leak hole and comparing the foregoing second required time with the foregoing determination base time obtained by multiplying the foregoing first required time by the above coefficient, it is possible to grasp the size of the leak hole as a failure on the basis of the magnitude of the above coefficient and the comparison in magnitude between the first required time and the second required time. In this manner, it is possible to practically determine the state of leak.
At the time of the first measurement and at the time of the second measurement, the amount of remaining fuel is not changed and hence the evaporation system is substantially equivalent, so it is possible to make a correct determination on the state of leak.
Further, in both of the first measurement and the second measurement, an initial pressure and a final pressure are specified pressures set previously, so even when the amount of remaining fuel is large and hence the volume of a space is small to which a pressure difference is applied, it is possible to correctly measure the state of change in pressure. Its effect is only to elongate the required time that is required for the pressure in the evaporation system to change from the first specified pressure to the second specified pressure. Thus, it is possible to substantially relax conditions allowing a proper leak check and to increase the frequency of determinations and to make a correct determination on the state of leak.
It is also recommended that the foregoing coefficient be set at the ratio of the total area of the leak points at the time of the first measurement that include the base leak hole and a leak hole as a failure to the area of the leak point at the time of the second measurement that includes only the leak hole as a failure at the time when the area of the leak hole as a failure is an allowable upper limit value.
The ratio of the foregoing second required time to the foregoing first required time is equal to the ratio of the area of the leak points at the time of the first measurement to the area of the leak point at the time of the second measurement. Here, if the foregoing coefficient is set at the ratio of the area of the leak points at the time of the first measurement to the area of the leak point at the time of the second measurement at the time when the area of the leak hole as a failure is the allowable upper limit value, it is possible to determine whether or not the area of the leak hole as a failure is smaller than its allowable upper limit value by whether or not the second required time is larger than the determination base time.
For example, if the allowable upper limit value of the area of the leak hole as a failure is the area of the base leak hole, in a case where the area of the leak hole as a failure is the allowable upper limit value, the ratio of the area of the leak points at the time of the first measurement to the area of the leak point at the time of the second measurement is two. Assuming that the coefficient is 2 by which the foregoing required time is multiplied when the determination base time is found, it is possible to determine that if the foregoing second required time is longer than the determination base time, the area of the leak hole as a failure is smaller than the allowable upper limit value and if the foregoing second required time is shorter than the determination base time, the area of the leak hole as a failure is larger than the allowable upper limit value.
In accordance with the second aspect of the invention, the pressure in the evaporation system is made the first specified pressure set previously, then the base leak hole is opened, and a required time is measured that is required for the pressure in the evaporation system to change from the first specified pressure to the second specified pressure set previously at a value closer to a pressure outside the evaporation system than the first specified pressure in a state where leak occurs at the base leak hole;
the pressure in the evaporation system is made the first specified pressure, then the foregoing base leak hole is closed, and a pressure reached in the evaporation system is measured when a determination base time obtained by multiplying the required time by a coefficient set previously based on the area of the base leak hole; and
the state of the leak in the evaporation system is determined by comparing the pressure reached with the second specified pressure.
In the first measurement of the first required time, the leak points in the evaporation system are the leak hole as a failure and the base leak hole and in the second measurement of the second required time, the leak point is only the leak hole as a failure. Thus, the rate of change in the pressure in the evaporation system is smaller at the time of the second measurement in which the area of the leak point is smaller. According to the Bernoulli""s theorem, the velocity of flow of gas at the leak point is equal if the pressure in the evaporation system is equal. Thus, when a time elapsing during a time period in which the pressure in the evaporation system changes from the same initial pressure to the same pressure is compared between the first measurement and the second measurement, the ratio of the time elapsing at the time of the second measurement to the time elapsing at the time of the first measurement is equal to the area of the leak points at the time of the first measurement to the area of the leak point at the time of the second measurement.
Here, the ratio of the area of the leak points at the time of the first measurement to the area of the leak point at the time of the second measurement depends on the ratio of the area of the leak hole as a failure to the area of the base leak hole which causes leak only at the time of the first measurement.
Thus, by setting the foregoing coefficient on the basis of the area of the base leak hole and comparing the foregoing pressure reached with the second specified pressure when the determination base time obtained by multiplying the foregoing required time by the above coefficient elapses in the second measurement, it is possible to grasp the size of the leak hole as a failure on the basis of the magnitude of the above coefficient and the comparison in magnitude between the foregoing pressure reached and the second specified pressure. In this manner, it is possible to practically determine the state of the leak.
At the time of the first measurement and at the time of the second measurement, the amount of remaining fuel is not changed and hence the evaporation system is substantially equivalent, so it is possible to make a correct determination on the state of the leak. Here, for example, when it is assumed that the coefficient is 2 by which the foregoing required time is multiplied when the determination base time is found, it is possible to determine that as the foregoing pressure reached has larger allowance for the second specified pressure, the leak hole as a failure becomes smaller in size than the base leak hole, and that as the foregoing pressure reached is larger than the second specified pressure, the leak hole as a failure is larger in size than the base leak hole.
Further, the rate of change in pressure in the second measurement is not so large as in the first measurement because only the leak hole as a failure causes the leak. Thus, if the foregoing coefficient is properly selected, even if the amount of remaining fuel is large and hence the volume of the space is small to which the pressure difference is applied, the pressure reached is not changed to the pressure outside the evaporation system. Moreover, as described above, since the rate of change in pressure is smaller in the second measurement than in the first measurement, it is easy to set the determination base time in such as way that the pressure reached does not become the pressure outside the evaporation system. Moreover, since the second measurement is finished regardless of the amount of leak at the time when the determination base time is reached, there is not presented a problem that as the amount of leak is smaller, a time period required to finish the measurement becomes longer, as is the invention claimed in claim 1. That is, a time period is not much varied that is required to perform the leak check. Thus, this can greatly relax conditions allowing the leak check and increase the frequency of determinations.
Here, in a case where the leak hole as a failure is so large that the quantitative estimation of leak is not required, needless to say, it is not always necessary to have allowance for the pressure outside the evaporation system when the determination base time elapses in the second measurement and it is recommendable to determine that the amount of leak is large when the pressure reaches a specified threshold within the determination base time.
It is recommended that the foregoing coefficient be set at the ratio of the total area of the leak points at the time of the first measurement that includes the base leak hole and the leak hole as a failure to the area of the leak point at the time of the second measurement that includes only the leak hole as a failure at the time when the area of the leak hole as a failure is an allowable upper limit value.
When the pressure in the evaporation system is changed to the second specified pressure in the second measurement and the time that elapses during an interval that the pressure in the evaporation system changes from the first specified pressure to the second specified pressure is compared between the second measurement and the first measurement, the ratio of the elapsed time at the time of the second measurement to the elapsed time at the time of the first measurement is equal to the ratio of the area of the leak points at the time of the first measurement to the area of the leak point at the time of the second measurement. Here, if the foregoing coefficient is set at the ratio of the area of the leak points at the time of the first measurement to the area of the leak point at the time of the second measurement at the time when the area of the leak hole as a failure is the allowable upper limit value, it is possible to determine whether or not the area of the leak hole as a failure is smaller than the allowable upper limit value by whether or not the pressure reached when the elapsed time at the time of the second measurement reaches the determination base time reaches the second specified pressure.
For example, if the allowable upper limit value of the area of the leak hole as a failure is the area of the base leak hole, in a case where the area of the leak hole as a failure is the allowable upper limit value, the ratio of the area of the leak points at the time of the first measurement to the area of the leak point at the time of the second measurement is two. Assuming that the coefficient is 2 by which the foregoing required time is multiplied when the determination base time is found, it is possible to determine that if the pressure reached does not reaches the second specified pressure, the area of the leak hole as a failure is smaller than the foregoing allowable upper limit value and if the foregoing pressure reached is larger than the second specified pressure, the area of the leak hole as a failure is larger than the allowable upper limit value.
It is also recommended that the pressure difference be produced by increasing the pressure in the evaporation system to make the state of change in pressure the state of decrease in pressure.
It is also recommended that the pressure difference be produced by decreasing the pressure in the evaporation system to make the state of change in pressure the state of increase in pressure.
In accordance with the third aspect of the invention, there is provided a failure diagnosis device for diagnosing an evaporated fuel treating unit, which comprises:
a passage for making the evaporation system communicate with an atmosphere;
throttling means mounted in the passage and having a certain passage cross-sectional area;
a valve for closing the passage;
first required time measuring means that controls the pressure difference producing means and the valve to make the pressure in the evaporation system a first specified pressure set previously, then opens the valve, and measures a first required time that is required for the pressure in the evaporation system to change from the first specified pressure to a second specified pressure set at a value closer to a pressure outside the evaporation system than the first specified pressure;
second required time measuring means that controls the pressure difference producing means and the valve to make the pressure in the evaporation system the first specified pressure, then closes the valve, and measures a second required time that is required for the pressure in the evaporation system to change from the first specified pressure to the second specified pressure; and
determination means that determines the state of leak of the evaporation system by comparing the second required time with a determination base time obtained by multiplying the first required time by a coefficient set previously based on the passage cross-sectional area of the throttle means.
According to this aspect, it is possible to practically and correctly determine the state of leak and further to substantially relax conditions allowing a proper leak check and to increase the frequency of determinations.
It is also recommended that the foregoing coefficient be set at the ratio of the total area of leak points when the first required time is measured which includes the throttling means and a leak hole as a failure to the area of the leak point when the second required time is measured which includes only the leak hole as a failure at the time when the area of the leak hole as a failure is an allowable upper limit value.
In accordance with the fourth aspect of the invention, there is provided a failure diagnosis device for diagnosing the evaporated fuel treating unit, which comprises:
the passage for making the evaporation system communicate with an atmosphere;
the throttling means mounted in the passage and having a certain passage cross-sectional area;
the valve for closing the passage;
required time measuring means that controls the pressure difference producing means and the valve to make the pressure in the evaporation system the first specified pressure set previously, then opens the valve, and measures a required time that is for the pressure in the evaporation system to change from the first specified pressure to the second specified pressure set previously at the value closer to the pressure outside the evaporation system than the first specified pressure;
pressure reached measuring means that controls the pressure difference producing means to make the pressure in the evaporation system the first specified pressure, then closes the valve, and measures pressure reached in the evaporation system when a determination base time elapses that is obtained by multiplying the required time by a coefficient set previously based on the passage cross-sectional area of the throttle means; and
determination means that determines the state of leak of the evaporation system by comparing the pressure reached with the second specified pressure.
According to this aspect, it is possible to practically and correctly determine the state of leak and further to substantially relax conditions allowing the proper leak check and to increase the frequency of determinations.
Here, in a case where the leak hole as a failure is so large that the quantitative estimation of leak is not required, needless to say, it is not always necessary to have allowance for the pressure outside the evaporation system when the determination base time elapses in the measurement of the pressure reached and it is recommendable to determine that the amount of leak is large when the pressure reaches a specified threshold within the determination base time.
It is also recommended that the foregoing coefficient be set at the ratio of the total area of the leak points when the foregoing required time is measured which includes the throttle means and the leak hole as a failure to the area of the leak point when the pressure reached is measured which includes only the leak hole as a failure at the time when the area of the leak hole as a failure is the allowable upper limit value.
It is also recommended that the foregoing pressure difference producing means be so constructed as to be means for increasing the pressure in the evaporation system to make the state of change in pressure the state of decrease in pressure.
It is also recommended that the foregoing pressure difference producing means be so constructed as to be means for decreasing the pressure in the evaporation system to make the state of change in pressure the state of increase in pressure.
It is also recommended that the foregoing pressure difference producing means be constructed by a motor-driven pump. In this case, the pump can be operated without the power of the internal combustion engine, so even when the engine is stopped, it is possible to perform the leak check and hence to increase the frequency of determinations.
It is also recommended that the failure diagnosis device further includes prohibition means that determines whether or not the internal combustion engine is in the state of operation and when it is in the state of operation, prohibits operations of the required time measuring means and the pressure reached measuring means.
During the operation of the internal engine, sometimes, the fuel is shaken by vibration to be abruptly evaporated and a fuel pump arranged in the fuel tank is heated to produce a sudden change in temperature. For this reason, there is a fear that a correct determination on the state of leak could not be preformed. According to the prohibition means, it is possible to eliminate the causes of error of determination and to perform the leak check correctly.